1. Field of the Invention
The present invention relates to a method of controlling a multiple cooling compartment refrigerator, preferably of the type having a variable capacity compressor or a refrigerant flow rate control valve.
2. Description of the Related Art
A kind of refrigerator having a great success in the domestic appliance market is the one having a fridge and a freezer unit in a cabinet with a single compressor. This success is due on one side to versatility of such solution (two compartments at different temperatures, two doors) and on the other side to the lower price of such refrigerator that has a single compressor and a single refrigeration circuit, if compared to a dual compressor refrigerator.
The drawback of this technical solution is a not easy independent control of temperatures in the fridge compartment and in the freezer compartment.
The temperature control of a freezer compartment (FZ) or a refrigerator compartment (FR) is generally obtained, in case of an appliance having electronic control circuit and in case of use of a variable cooling capacity compressor, by adjusting the compressor cooling capacity on the basis of the temperature error parameter. Another way of controlling temperatures of refrigerator compartments is to adjust the flow rate of the refrigerant delivered to the evaporator by means of a flow rate control valve, or to adjust the cooling-air flow delivered to compartments through a movable damper. The classical control logic is PID based, meaning that the Proportional, Integrative and Derivative parts of the temperature error variable are taken in consideration in the negative feedback system to adjust the output variable up to obtain the needed temperature. The attached FIG. 1 shows a case in which the PID negative feedback control system is used to control the temperature of a single compartment refrigerator. The input of the PID control block is the Temperature Error (difference between the target temperature and the actual one) and the output is directly converted in cooling capacity request. The sensed temperature can be either the temperature inside the compartment or the temperature of one or more predetermined zones of the evaporator. A dedicated inverter will receive the cooling capacity request signal as input and will have the task to drive the compressor keeping under control the cooling capacity (such compressor being either of the type having a variable speed or of the type with a variable displacement, i.e. the so-called linear compressor).
In case of multiple compartments and a single compressor available, the control of the temperatures becomes more critical. One of the known solution for a dual compartment refrigerator, disclosed in EP-A-859208, comprises two temperature sensors, one in the refrigeration chamber forming part of the control circuit made to stop and start the compressor, the other in the freezing chamber forming part of the control circuit made to control the speed of the compressor.
FIG. 2 shows the condition according to another solution in which the control operates in a case of a dual compartment refrigerator. The two blocks “FR_Controller” and “FZ_Controller” can be two PID-like controllers and each of them computes the “Cooling Capacity Request” to be provided to the compressor, necessary for controlling the temperature of the respective compartment refrigerator (FR) or freezer (FZ). The “Cooling Compartment Management” is a control block used to establish the direction and/or the flow rate of the refrigerant, or in case of a refrigerator cooled by cooling air (typical the case of so-called side-by-side refrigerator), the position of a damper which splits the air flow between the freezer and the fresh food compartments. In the above first case, the “V” device is a valve receiving the command and delivering totally or partially the refrigerant across the refrigerator evaporator and/or the freezer evaporator. Ideally, the controller has multiple control tasks: firstly the controller has to keep the temperatures set by the user and, secondly, the controller has to be able to efficiently drive the compressor and the valve V to keep the energy consumption as low as possible. However, in case of independent controls (as shown in FIG. 2) the solution may be very complicated or even impossible if the energy consumption has to be kept low.